1. Field of the Invention
The present invention relates to a liquid crystal display (LCD). More particularly, the present invention relates to a switching voltage controlling circuit of an LCD.
2. Description of Related Art
As the photoelectric industry advances, LCDs have been applied extensively to various kinds of electronic products. It should be mentioned that the LCD can barely provide equivalent switching voltages to each pixel unit due to the increasing dimension of a display panel of the LCD, and color errors then occur between blocks of the display panel. Detailed descriptions accompanying drawings are provided hereinafter.
FIG. 1A is a schematic view of a conventional LCD. FIG. 1B is a schematic view of a pixel unit of the conventional LCD. Referring to FIGS. 1A and 1B, an LCD 10 has a normally white frame when liquid crystals contained in the LCD 10 are not driven. The LCD 10 is composed of a display panel 40, a plurality of source drivers 20, and a plurality of gate drivers 31, 32, and 33. The source drivers 20 are coupled to each pixel unit 41 through source driving lines 101. On the other hand, the gate drivers 31, 32, and 33 are coupled to each of the pixel units 41 through gate driving lines 111, respectively. Each of the pixel units 41 includes a transistor 121, a storage capacitor 122, and a pixel capacitor 123.
FIG. 2 is a curve illustrating a relationship between a source driving current Id and a switching voltage Vg. Referring to FIGS. 1A, 1B, and 2, the gate drivers 31, 32, and 33 receive a constant voltage VGL and thereby generate the switching voltage Vg for controlling each of the pixel units 41. It should be noted that a transmission line 131 of the display panel 40 has a line resistance, and therefore the constant voltage VGL received by the gate driver 31 is slightly greater than the constant voltage VGL received by the gate driver 32. Besides, the constant voltage VGL received by the gate driver 32 is slightly greater than the constant voltage VGL received by the gate driver 33.
Based on the above, the switching voltage Vg provided by the gate driver 33 to the pixel unit 41 is slightly less than the switching voltage Vg provided by the gate driver 32 to the pixel unit 41, and the switching voltage Vg provided by the gate driver 32 to the pixel unit 41 is slightly less than the switching voltage Vg provided by the gate driver 31 to the pixel unit 41. Owing to the difference in the switching voltage Vg respectively received by each block of the display panel 40, the color errors may arise between the blocks of the display panel 40. Specifically, when the LCD 10 displays frames at the same color level, the pixel unit 41 of the gate driver 33 of the LCD 40 is somewhat brighter than the pixel unit 41 of the gate driver 32, and the pixel unit 41 of the gate driver 32 of the LCD 40 is somewhat brighter than the pixel unit 41 of the gate driver 31. The above description is, for instance, exemplified in FIG. 3 that is a schematic view of a display panel in which color errors occur between the blocks.
FIG. 4 is a schematic view of another conventional LCD. In order to prevent the color errors occurring between the blocks of the display panel, a solution in which a current-limiting resistor 141 is additionally disposed between the constant voltage VGL and the gate driver 31 is proposed according to the pertinent art. After the current-limiting resistor 141 is disposed, the equivalent resistance of the transmission line 131 is increased, and a current passing through the transmission line 131 is then decreased when the constant voltage VGL remains unchanged. As a result, the voltage difference in the constant voltage VGL respectively received by the gate drivers 31, 32, and 33 is reduced. As such, the difference in the switching voltage Vg respectively generated by the gate drivers 31, 32, and 33 is reduced as well. The color errors occurring between the blocks of the display panel 40 are then eliminated.
Nevertheless, the occurrence of color errors between the blocks of the display panel 40 can only be precluded by employing the current-limiting resistors 141 with different resistance values when different display panels 40 are used. That is to say, given that different types of the display panels 40 are used, the display panel manufacturers must find the proper resistance value for each type of the display panel by way of trial and error, which is time-consuming and inconvenient.